A morphometric study of the density of mitochondrial cristae in heart and liver of aging mice.

Mitochondria in sections of left ventricular wall and liver from C57BL/6J mice, 9, 18, and 36 mo. old, were analyzed using stereological procedures. At 9 mo. of age mu2 cristae surface per mu3 cytoplasm(Sv-c/c was fivefold greater in heart compared with liver reflecting the larger values in the former for both mu2 cristae surface per mu3 mitochondrion (Sv-c/m) and mu3 mitochondria per mu3 cytoplasm (Vv-m):Sv-c/c = Sv-c/m. Vv-m. At 36 mo. in both tissues, Sv-c/c had decreased to 65% of the earlier value. This was due to a decrease in Vv-m alone in heart and both Vv-m and Sv-c/m in liver. In both tissues the number of mitochondria per mu3 cytoplasm (Nv-m) also decreased with age while mu3 organelle average volume (vm) remained constant, supporting previous observations: Vv-m = Nv-m-vm. These data support the views: different tissues in the same organism age independently; and mitochondrial inner and outer membranes have a semi-independent existence.